This application claims priority to Swedish Application No. 0000220-4, filed Jan. 26, 2000, which is expressly incorporated herein by reference.
The invention relates to a supercharged internal combustion engine having a cylinder block, a cylinder head, a crankcase containing oil and an air intake conduit. The air intake conduit communicates with air intake channels in the cylinder head, and which is connected to a supercharging unit and a throttle valve located downstream of the supercharging unit. A first evacuation conduit is provided that connects the crankcase and the air intake conduit via a pressure regulator at a point downstream of the throttle valve for evacuating gases, so called xe2x80x9cblow-byxe2x80x9d, from the crankcase. A second evacuation conduit connects the crankcase to the air intake conduit at a point upstream of the supercharging unit. A device for separating oil from the evacuated blow-by gases is also provided. At least one further evacuation conduit is provided which can connect a collecting vessel, or another source of harmful emissions, with the evacuation conduits. Non-return valves are provided in the first and second evacuation conduits in order to prevent gases from flowing back into the crankcase.
It is a known that it is not possible to achieve a piston ring seal, between a piston and a cylinder wall, which gives a complete sealing effect between a combustion chamber and a crankcase during normal operation of an internal combustion engine. A certain amount of combustion gases, hereinafter termed xe2x80x9cblow-byxe2x80x9d, will, with few exceptions, flow past the piston rings into the crankcase of the engine. In order to avoid a high positive pressure in the crankcase, it must be ventilated, whereby the gases are removed leaving a low positive pressure, or a slight negative pressure in the crankcase.
Preferably, the crankcase is ventilated to atmospheric pressure, but for environmental reasons, it is not suitable to ventilate the gases directly to the surrounding atmosphere. In order to use the existing purification equipment of the engine, the blow-by must be returned to the combustion chamber, which is achieved by leading the gases into intake conduit(s) of the engine where the blow-by is mixed with the induction air. The simplest way of achieving this is to connect an evacuation conduit from the crankcase to the intake conduit at a point before the supercharging unit. At this point, between the intake air filter and the supercharging unit, the air pressure will be atmospheric, or near atmospheric. Although an oil separator of some form has traditionally been used, it has been inevitable that a certain amount of oil vapor has been included in the blow-by from the crankcase, through the evacuation conduit and into the supercharging unit. This oil vapor may condense and collect in the supercharging unit, and, depending on the amount of oil and the temperature, may disturb the function of the supercharging unit. In those cases where an intercooler is connected between the supercharging unit and the intake conduit, there is a risk of clogging the cooling channels causing a deterioration of the function of the intercooler.
The problem of oil collecting in the supercharging system can be avoided by connecting the evacuation after the throttle valve. There is often a significant negative pressure in this part of the conduit, however, especially at low engine load, which may cause an undesirable, very low negative pressure in the crankcase. In addition, it is not possible to evacuate the blow-by to this point of the conduit when the engine is being supercharged. One method for solving this problem, at least in part, is to use two evacuation conduits. One conduit is connected before the supercharging unit and one before the throttle valve. The latter is connected to the intake conduit via a throttling device, which limits the flow to the intake conduit, and a non-return valve which prevents flow in a direction away from said conduit. It is, however, difficult to achieve a balance in a system of this type, both for a normally aspirated engine, which has a negative pressure in the intake conduit at all times, and for a supercharged engine, which has a negative pressure in the intake conduit at low load and a positive pressure at high load. In one crankcase ventilation system for a supercharged engine, the evacuation conduit is connected to the intake conduit upstream of the supercharging unit and is provided with a pressure regulator arranged to maintain an almost constant pressure approximately equal to atmospheric pressure in the crankcase. At high load, gases will flow through the latter evacuation conduit to the suction side of the supercharging unit. Under this condition, there will be a positive pressure in the intake conduit, downstream of the throttle, causing the non-return valve in the other evacuation conduit to close and prevent air from flowing back into the crankcase. At low load and subsequent negative pressure downstream of the throttle valve, blow-by gases from the crankcase will flow via the non-return valve and the throttling device to the intake conduit. Under certain operating conditions, however, air may simultaneously be sucked from the intake conduit upstream of the supercharging unit, via the pressure regulator, to the intake conduit downstream of the throttle valve. Such an alternating flow of hot gases and cold air in opposite directions may result in condensation and a risk of freezing during cold weather conditions. One solution to this problem is to use a heating coil containing hot coolant around the evacuation conduit upstream of the throttle valve, although this adds to the cost of the system.
A similar problem occurs during evacuation of the vehicle canister. The canister is used for absorbing fuel vapor from the fuel tank in order to avoid ventilation of vapors to the atmosphere. Especially during filling of the tank, or during periods of high ambient temperatures, it is necessary for the canister to be able to absorb relatively large amounts of fuel vapor. The function of the canister itself is well known and will not be described here, in detail. In order to avoid saturation of the canister, it must be provided with an evacuation conduit, which, using negative pressure, sucks vapor from the canister, via a ventilating valve, to the induction system of the engine. A known solution is to split the evacuation conduit into two branches after the ventilating valve. A first conduit is connected downstream of the throttle valve and a second conduit is connected upstream of the supercharging unit, whereby each conduit is provided with a non-return valve.
Due to the degree of packing; i.e., the space used for assembly and installation of the engine and engine compartment components in relation to the available space, the introduction of new components and changes in the positioning of existing components is a problem. A new component can, for instance, be a system for purification of exhaust gases from the vehicle in front, whereby induction air, air for the passenger compartment and air passing through the engine compartment can be purified with respect to particles, nitrous oxides, etc. Such a system would require further conduits, and in certain cases, needs to be ventilated into the induction system of the engine.
The present invention, in its several disclosed embodiments, alleviates the drawbacks described above with respect to combined crankcase and canister ventilation systems and incorporates several additional beneficial features.
An object of the invention is to provide a supercharged combustion engine with pressure regulated crankcase ventilation, which eliminates the problems cited above. According to the invention, this is achieved by way of a combustion engine as described above, wherein the first and second evacuation conduits are connected in communication with a pressure regulator arranged to maintain a substantial constant pressure in the crankcase. Both evacuation conduits are provided with valves arranged to limit or prevent the flow of gases from the intake conduit to the crankcase. In addition, the system is provided with at least one further evacuation conduit, which can be used for ventilation of a collecting vessel of emissions, and the like, and is connected to the first and second conduits at a point between the pressure regulator and the valves.
According to the invention, pressure regulated crankcase ventilation is achieved both when the engine is normally aspirated (low load) and when it is supercharged (high load). During normally aspirated operation, virtually all blow-by will pass through the first evacuation conduit to the intake conduit downstream of the throttle, as the valve(s) in the second evacuation conduit prevents or limits the flow of intake air in the opposite direction; i.e., to the crankcase. During supercharged operation, with a positive pressure in the intake conduit, virtually all blow-by instead passes through the second evacuation conduit to the intake conduit upstream of the supercharging unit, as the valve means in the first evacuation conduit prevents or limits the flow from the intake conduit towards the crankcase.
By interconnecting existing evacuation conduits with further evacuation conduits for other types of emissions; for example, from a canister for fuel tank vapors or a catalytic purification device for cleaning ambient air, the number of new conduits and the accompanying couplings for the connection of these may be reduced significantly. This will simplify the installation of conduits, reduce the number of possible sources of leakages, and have a positive effect on the degree of packing of the engine. This is particularly true regarding the intake manifold, where it is often difficult to find room for more than one connection. Further advantages are that the system gives a stable negative pressure in the crankcase, and that the system diagnostics will be reliable, since a leakage exceeding the normal flow in any of the conduits will cause the engine to stop during idling, due to the large influx to the intake conduit. The emissions may be supplied continuously to the evacuation conduits, or be collected in a container in some form, such as a canister or a regenerative catalytic converter, for subsequent intermittent ventilation. In the latter case, a regulated valve is often required in order to control to the flow to the evacuation conduit.